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Scientists at the University of California, San Francisco and the University of California, Davis have completed the first clinical trial of a new cancer drug in pet cats, offering hope for a disease that has long been nearly impossible to treat. The found 35 percent of the cats with squamous cell carcinoma who received treatment had their disease controlled with minimal side effects. The drug will likely be effective for humans with head and neck squamous cell carcinoma. The was published today in Cancer Cell.

Oral squamous cell carcinoma is one of the most aggressive cancers in cats. Most cats survive only two to three months after diagnosis, since surgery, chemotherapy and radiation usually do little to stop it.

“One of the struggles I’ve had my entire career is that cats with this cancer—there is really nothing we can do,” said second author Katherine Skorupski, a professor of clinical medical oncology with the �鶹app��� School of Veterinary Medicine. “We see these cats, we give the bad news, and we do our best to keep them comfortable until they are euthanized. So the fact that we would have something, anything, that might help these cats is so exciting.” 

She said in the future, the drug will likely be used with other therapies. Cats, who often don’t get much attention in cancer research, could benefit greatly.

The drug, which was originally designed to treat human head and neck cancers, is the first of its kind to target a protein called STAT3. This protein acts like a faulty switch that tells cancer cells to keep growing. 

“What’s exciting is that this study shows it’s possible to shut down a protein that drives cancer,” said first author Daniel Johnson with the University of California, San Francisco Helen Diller Family Comprehensive Cancer Center. “That has been notoriously difficult in the past.” He added that the study also shows that pets with cancer can be good models of human disease and they may yield more reliable results than mouse models. 

The idea to test the drug in cats came from a discussion first author Jennifer Grandis, with UCSF, had with her sister, a veterinarian. She learned that oral cancers are extremely difficult to treat. The UCSF researchers coordinated with veterinarians at �鶹app��� to recruit pets for the trial.

More time with family

One cat who benefitted from the trial was Jakiro, or “Jak,” a 9-year-old black shorthair. His owner, Tina Thomas, was devastated when told he had only 6 to 8 weeks to live. 

“It was just a gut punch,” she said. “We wanted more time with him. When I found out about this clinical trial, I knew I wanted him to be a part of it.”

Jak received weekly treatments for a month. His symptoms improved, and he went on to live more than eight months—long enough to spend another Christmas with his family. 

“It was invaluable to us to give him time where he was comfortable and could enjoy being around his family,” Thomas said. “He loved being under our Christmas tree and giving him that one more Christmas, which I don’t think he would have had otherwise, just made us feel good.”

Cats as models

Other than mild anemia, none of the cats in the trial developed side effects that were attributable to the treatment. Of the 20 cats that were enrolled, 7 of them exhibited either a partial response or stable disease during the study period. Among the 7 that responded, the average survival pos-treatment was 161 days.

Importantly, the treatment appeared to not only block the activity of STAT3 but also raise levels of a protein associated with an immune response to cancer.

“By partnering with veterinary oncologists and doing clinical trials in companion animals, we can learn an enormous amount about how these drugs work while also helping people’s pets. None of the cats in these trials were harmed, and many of them benefited,” Grandis said.

Researchers are currently working with a small biotech company to advance the new compound in clinical trials for both pets and humans.

Other �鶹app��� authors include Robert B. Rebhun, Daniel York, Hong Chang, and Ellen E. Sparger.

This work was supported by the National Institutes of Health and the Center for Companion Animal Health at �鶹app���.